1. Field of the Invention
This invention relates to exhaust gas sensors as used in the control of the air and fuel mixture in an internal combustion engine and more particularly to a system for the detection of the failure of such an exhaust gas sensor.
2. Description of the Prior Art
The use of an exhaust gas sensor in exhaust systems of internal combustion engines for controlling the air/fuel ratio to the engine is well known as exhibited in the U.S. Pat. No. 3,745,768 issued to Zechnall et al. and entitled "Apparatus To Control The Proportion Of Air and Fuel In The Air/Fuel Mixture of Internal Combustion Engines." In this particular patent an oxygen analyzer or exhaust gas sensor is responsive to the oxygen present in the exhaust gas of an internal combustion engine. A signal is generated by the sensor indicating whether or not oxygen is present in the exhaust gas and this signal is supplied to an electronic control unit for controlling or supplying information to control the amount of fuel injected into the cylinder of the internal combustion engine. If the sensor indicates that oxygen is present in the exhaust gas the sensor signal will supply information to the control unit to increase the amount of fuel supplied to the internal combustion engine. Conversely, if the sensor indicates a lack of oxygen in the exhaust gas it will supply information tending to reduce the amount of fuel supplied to the cylinder.
Such control is necessary for an internal combustion engine to improve the performance of the engine and to control the quality of the exhaust gas components in the exhaust gas of an internal combustion engine.
The use of exhaust gas sensors in the exhaust lines of furnaces is likewise old in the art. Again the purpose of such sensors in the exhaust lines is to control the operation of the furnace for better performance and economy.
Oxygen sensors are used in the steel making processes to determine the amount of oxygen contained in the molten steel in the process of manufacture. These sensors generate signals which are applied to a control unit to control the process in the steel making.
In such instances of the prior art, detection of a failed sensor has been primarily one of observation by an operator such as by the ultimate failure of a component such as a converter downstream of the sensor or the physical destruction of the sensor by the environment in which it is placed. Constant or periodic monitoring of the output voltage of the sensor under controlled conditions has been required in order to determine whether or not the sensor is operating or performing correctly.
In fuel management systems for internal combustion engines it is necessary to accurately control the fuel/air ratio entering the engine in order to control the products of combustion as they appear in the exhaust gases. It is desired in the exhaust gas of internal combustion engines to control the amount of unburnt hydrocarbons and carbon monoxides by regulating the fuel/air mixture to the cylinder of the engine. Nitrogen compounds in the exhaust gases are another undesirable component which may be neutralized by a catalytic converter placed downstream of the gas sensor. With the gas sensor controlling the fuel/air ratio into the engine thereby controlling hydrocarbons and carbon monoxide in the exhaust gas the catalytic converter need only have a single bed for neutralizing nitrogen compounds.